System for magnetizing using an a.c. to d.c. converter



Oct. 20, 1970 w, p. PTOMEY ET AL 3,535,621

SYSTEM FOR MAGNETIZING USING AN A.C. TO 13.0. CONVERTER Filed 0012. 18, 1967 INVENTORIS ATTORNEYS United States Patent 3,535,621 SYSTEM FOR MAGNETIZING USING AN A.C. T0 D.C. CONVERTER Willie P. Ptomey, 2294 Janette Drive, and Leland E.

Broyles, 1066 Rose Circle, both of Napa, Calif. 94558 Filed Oct. 18, 1967, Ser. No. 676,302 Int. Cl. G01r 33/12 US. Cl. 32434 1 Claim ABSTRACT OF THE DISCLOSURE The invention pertains to a device for furnishing direct current to a short length of conductor, as for testing the magnetic characteristics of a ferromagnetic conductor. More specifically, the invention relates to a system for converting alternating current at known potential, as 120 volts, 60 Hz. (cycles per second), to direct current at high magnitudes as between 200 to 700 amperes and further to supply this direct current to a conductor via a pair of parallel prods mounted in a handle.

An object of this invention is to provide a simple and compact system whereby a variable direct current of high amperage may be supplied to a pair of prods.

A further object of the invention is to provide a mechanism adjacent the prods to control, via a relay, the flow of current to the primary of a transformer, the secondary of which supplies current to a rectifier and the prods.

A still further object of the invention is to provide control means whereby the full or partial turns of the primary winding may be utilized.

Yet another object of the invention is to control the application of voltage to the primary of the transformer by the use of a silicon controlled rectifier.

Still another object of the invention is to supply cooling means for the transformer.

An yet another object of the invention is to supply an ammeter in the circuit preferably close to the prods to indicate the magnitude of current flow through the prods.

A further object of the invention is to supply a lighting means in the handle to illuminate the prods and the portion of the conductor to which the prods are applied.

Other objects will become apparent after a consideration of the following specification when read in conjunction with the accompanying drawing in which:

FIG. 1 is a wiring diagram of a circuit employed in carrying out the invention;

FIG. 2 is a diagrammatic view of a modified form of voltage control to the primary of the transformer;

FIG. 3 is a perspective view of a handle carrying the I prods; and

FIG. 4 is a cutaway view of the handle showing an indicator lamp and control push button therein.

Referring to the drawing, in FIG. 1 a plug is adapted to be plugged into a receptacle furnished with an ordinary A.C. supply, for example at 120 volts, 60 Hz. The plug is connected to wires 12 and 14. For simplicity of description wire 12 may be considered as the central wire of a three phase 240-volt system and at ground potential, the other wire 14 being the hot lead. Lead 14 is connected via a fuse or circuit breaker 16 to both poles 18 and 19 of a double pole, double throw, switch 20 having an intermediate circuit disconnect position, an upper circuit connect position and a lower circuit connect position.

Patented Oct. 20, 1970 When in either circuit connect position, a circuit is closed to a pilot lamp 21, current then flowing via the line 14, circuit breaker 16, right-hand pole 19 of the switch, lines 22 and 23, pilot lamp 21 and line 24 to the grounded line 12. Also current flows via the switch, line 22, line 25, fan motor 26 and line 27 to ground line 12, thus energizing the fan motor. A branch circuit further feeds current via line 28, a receptacle 30, plug 32 and line 34 to a lamp 36 in the handle of a testing probe 38 and thence via line 39, plug, 32, receptacle 30 and ground line 12.

When a normally open push button 43 in the handle is closed, current further flows via contacts in the push button and line 44 to plug 32, receptacle 30, line 45 to the rectifier diode 46, thence via line 47 to the coil of a relay 48 and then via line 49 to ground line 12, thereby energizing the relay and causing its contacts 50 to close. When the relay is energized and the switch 20 is closed in the down position, a circuit is completed as follows: From line 14, via fuse 16 to the left-hand pole 18 of switch 20 and then via line 51 through the full primary 52 of transformer 53, thence through the closed contact 50 of relay 48 to line 49 and thence to ground line 12, thereby energizing the primary winding of the transformer.

Upon energization of the primary winding of the transformer, the secondary winding 54 is energized, this secondary winding being connected to a pair of prods 55, 56 fixed in the handle 57 of the probe.

The circuit to these prods is as follows: From one pole of the secondary winding 54 to wire 58, diode 60, jack 62, plug 64 and flexible lead 65 to prod 55, the current (which is a magnetizing current for the ferromagnetic material under test) then flowing through the material 66 to prod 56, flexible lead 67, plug 68, jack 70, line 72, meter shunt block 74, and line 76 back to the opposite pole of the secondary of the transformer. Ammeter 77 bridges the block 74 and measures the current supplied to the prods.

Since the transformer secondary is designed to carry as much as 700 amperes of half-wave DC, a cooling thereof is desirable and is provided by appropriately positioned fan 78 which is driven by motor 26.

Since both the up and down right-hand side contacts of switch 20 are connected together, the fan is driven in either operative position of the pole 19 of the switch. Also, as stated heretofore, the pilot light 21 and indicator light 36 in the handle are lit in either of the two operative positions of the pole 19. Diode 46 is utilized in the circuit of the relay to subdue chatter or flutter of the contacts and diode 60 is utilized to provide half-wave rectified current at the prods. The current flow in the prods, with full primary, will be of the order of 700 amperes.

To provide a regulatable direct current at the prods of a lesser magnitude, a tap is provided in the primary winding of the transformer. This tap is connected to the A.C. supply through a silicon controlled rectifier whose gate is under potentiometer control and will enable a selected half-wave direct current of between 200 to 500 amperes to be applied to the conductor to which the prods are applied.

When the switch 20 is thrown to its up position, current will flow via pole or blade 18 to a line 80 and via silicon controlled rectifier (SCR) 82 to tap 84 on the transformer primary. Gate 86 of the silicon controlled rectifier is connected to a phase shifting system comprising a diode 88 connected to manually controlled potentiometer 90, capacitor 92, and line 94 connected to one of the contacts of relay 48 so as to render the phasing system inoperative when the relay is deenergized.

Gate electrode 86 of the silicon controlled rectifier is connected between a pair of resistors 96, 98 bridging the capacitor, resistor 96 being a current limiting resistor and resistor 98 being a compensatory resistor, its magnitude depending on the particular gating operation of the rectifier which may vary somewhat even in rectifiers of the same type. When the relay 48 is closed by operation of push button 43, the circuit for the SCR and the phasing circuit is completed via contact 50 and line 49 back to line 12.

A second form of control of the current fiow through the prods is disclosed in FIG. 2. FIG. 2 shows only so much of what is shown in FIG. 1 as is necessary to an understanding of the control of voltage to the transformer primary, the remainder of the circuit of FIG. 1 remain ing unaffected.

In the form of transformer control illustrated in FIG. 2, diode 101 senses the voltage at the primary winding, that voltage varying in accordance with whether or not a load is impressed on the secondary. When the prods and 56 are applied to a conductor, there is a voltage drop in the primary of the transformer and the voltage at the cathode of the diode 101 decreases. Therefore the voltage at diode 101 serves as a reference voltage. The control of the transformer primary is therefore responsive to the functioning of the secondary of the transformer.

The circuit operates by comparing the residual back EMF on diode 101 in series with the gate of SCR 82 and ultimately with the primary winding 52, with the circuit generated reference voltage, this being the result of the divider network composed of trimmer resistor 102 and resistors 104 and 106 and potentiometer 108, the potentiometer being bridged by a capacitor 109. Current flows in this branch only during the positive half cycles due to the conduction of diode 100. A current limiting resistor 110 is interposed between the potentiometer and the diode The flow of current through the resistor is a half sine wave.

If the residual back EMF applied to diode 101 is greater than the voltage applied to the anode of the diode,

as when the prods are not in contact with the conductor 66, the diode will be back biased and the SCR 82 will not be triggered; therefore the SCR will not supply power during this half cycle. As the back EMF drops, as when the prods are applied to the conductor 66, current again flows through the diode 101. The amount of current flow at the prods at which this occurs may be varied by changing the magnitude of the resistors in the branch circuit and by adjusting the tap on the potentiometer 108, which in effect causes, a phase shift in the current supplied to the gate of the SCR. By using this method of phase control, which triggers the SCR at any point from the beginning of the half cycle to the midpoint of the half cycle, together with the circuit as a whole, the current output at the prods can be varied from 200 to 500 amperes.

When the transformer 53 is loaded by contact of the conductor made by the prods, the back EMF drops causing the voltage at resistor 112 to be greater than the voltage at the gate of SCR 82. When this happens early in the cycle, more current is supplied to the transformer. If, however, it becomes desirable to have less output at the prods, a large capacitor 111 could be utilized to bridge one or more of the resistors, as resistor 104, in the bridge circuit to slow the buildup of potential at the gate of the SCR and to alleviate hunting action thereat. A compensating resistor 112 may be utilized between the gate and cathode of the SCR to :balance out SCR operation due to variations in manufacture.

Referring now to FIGS. 3 and 4, it will be noted that the handle 57 may be made of plastic tinsulating material, roughly in the form of a hollow rectangle with a rounded hand grip portion 120. The prods 55 and 56 are rods of copper or other good conductive material having upper ends screwed into the bottom of ferrules 122 and 123 firmly embedded in the plastic material. These ferrules are internally threaded at the lower ends as indicated at 124 and hollow at the upper ends 125 for insertion Cit therein and firm connection with the flexible leads 65 and 67. Additional ferrules 126 are spaced along the bottom and connected by a bus bar 127 with the ferrule 122, these additional ferrules being threaded for receiving the prod 56, in order to attain any desired spacing between the prods 55 and 56. Obviously, other means for securing the desired spacing of the prods may be utilized. Also fixed in the handle is the lamp base for lamp 36 and the spring biased open push button switch 43.

It will be obvious to one skilled in the art that various changes may be made in the described embodiment of the invention without departing from the spirit and scope thereof and therefore the invention is not limited by that which is illustrated in the drawings and described in the specification, but only as indicated in the accompanying claims.

What is claimed is:

1. An infinitely variable controlled magnetizing system for converting alternating current to a low voltage high amperage direct current, said system comprising a transformer having a high voltage primary winding and a low voltage secondary winding, an alternating current supply, means for connecting said alternating current supply to said primary of said transformer, a pair of test prods having means to adjust the spacing therebetween and adapted to receive various dimensional test specimens, wiring connecting the test prods with said secondary winding, a rectifier in said wiring for converting low voltage alternating current to pulsating direct current, a first switch operatively connected to said prods, a relay being connected to said alternating current supply including a coil to be energized and having contacts, said coil being operatively connected in series with said first switch and said contacts in series with said alternating current supply and with said primary winding, such that upon the actuation of said first switch, said relay coil energizes and closes its contacts whereby said alternating current supply is applied to said primary winding of said transformer wherein said direct current will appear across said pair of test prods, means including a tap on the primary winding of said transformer, and a silicon con trolled rectifier circuit having an input and an output, said output connected to said tap, said silicon controlled rectifier circuit including a gate electrode and means connected thereto for varying the current applied to said gate electrode, and said means for connecting said alternating current supply to said primary winding including a second switch, said second switch comprising a double pole, double throw, switch with the poles electrically interconnected, said switch connected in series with the alternating current supply and the primary winding, one of said poles effecting current flow through the full primary winding in one closed position of said second switch and current flow through the tapped primary winding by Way of the silicon controlled rectifier circuit in a second closed position of said second switch, the other pole in both closed positions completing the circuit to said first switch.

References Cited UNITED STATES PATENTS 2,481,937 9/1949 Mages 32438 2,529,118 ll/1950 Tschumi 3l7-l50 2,644,921 7/1953 Lewkowski 324-38 3,346,778 10/1967 Schroeder et al 317-123 3,378,762 4/1968 Parker 324-38 FOREIGN PATENTS 199,906 10/1958 Austria.

ALFRED E. SMITH, Primary Examiner R. J. CORCORAN, Assistant Examiner US. Cl. X.R. 

